The invention relates generally to a reprographic fusing device for fixing a toner image to a substrate. More specifically, the invention relates to a fusing device that is continuously movable relative to the print medium during printing.
In electrostatic printing, a dry marking material, such as toner, is fused to a substrate, such as a paper sheet. Fusing occurs when the substrate is subjected to pressure and/or heat to permanently affix the marking material to the substrate. Most common electrostatic printers use a fuser roll and a pressure roll that form a nip for the substrate to pass through. In many such printers, a variety of different size sheets may be passed through the nip of the rollers.
All conformable rolls suffer from surface wear, especially where the edges of the sheets contact the roll surface. FIG. 1 shows how the edges and body of 11″ and 14″ sheets of paper are distributed along the surface of a fuser roll in the axial direction in printers without a registration distribution system. In such printers, the sheet edges produce a stress concentration as they pass through the fuser nip under pressure, causing the thin surface coating on the roll, as well as the elastomeric layer under the surface, to degrade. The degradation of the roll is often manifested as a narrow area of lower gloss from a lead edge to a trail edge across the print fused to the substrate. In the context of mixed paper sizes, a 14″ print often shows a differential gloss streak 11″ in from the outboard (registered) edge. Such artifacts become visible to the customer after only a few thousand prints have passed through the fuser, far short of the target life of the roll.
One proposed solution to such problems is to change fuser rolls to accommodate different size papers. However, this method is not always practical or in keeping with existing program goals. For example, if only one paper size is run for a given roll set, the edge wear exists, but is outside the normal visible area of the print and goes unnoticed.
Another proposed solution is provided in U.S. Pat. No. 5,323,216 which discloses a lateral moving fuser station. The lateral moving fusing station is an intelligent system in which detection of incoming paper size is utilized to reposition the roll in an axial direction based on usage demographics, such that the location of edge wear is spread over a larger area.
The station includes a pressure roller and a heated fusing roller that are in pressure contact with each other to form a fusing nip. The fusing station is mounted on a base plate and is moved by a stepping-type drive motor controlled by a control and logic circuit. The control and logic circuit either activates the stepping motor prior to the start of a copy cycle for a set time period to move the fuser station laterally a pre-set distance, or activates the motor after a pre-set volume of copies have been fused. This way, if most of the paper run is 11 inches wide, a discrete or specific location within the 3 inches of roll from the 11 inch position to the 14 inch position can be made available for edge redistribution. However, by restricting lateral movement of the fusing station as described, productivity may be slowed due to the necessity to move to the fusing station during a print operation, such as when the pre-set volume of copies have been fused. Furthermore, banding may also result from the use of such discrete stepping systems.
These and other known methods have drawbacks which severely limit any performance benefits from existing registration distribution systems. For example, by moving the fusing station only between copy runs or interframes a pre-set distance, the fuser roller will suffer unnecessary wear at the point where the edges of the sheets contact the roll surface. The wear will continue to manifest itself as a narrow area of lower gloss from lead to trail edge across the print.